1. Technical Field
The present invention relates to an identity authentication device and a fingerprint sensor.
2. Related Art
An identity authentication device equipped with a fingerprint sensor has been known. As common sensing measures in such fingerprint sensor, there are a resistance detecting type, a photoelectric type, a piezoelectric type and a capacitance type.
The capacitance type fingerprint sensor detects a fingerprint pattern by determining capacitance which varies due to a distance between the fingerprint having concavity and convexity and a detection surface. The capacitance type fingerprint sensor can be easily contained in a thin and small package since it does not require a light source. Japanese Unexamined Patent Publication No. 2001-56204 is a first example of related art and Japanese Unexamined Patent Publication No. 2001-133213 is a second example of related art. Such capacitance type fingerprint sensor is disclosed in, for example, the first and second examples.
Generally, a dielectric thin film having a thickness of about 200-500 mm is formed on the detection surface to which the fingerprint contacts in the capacitance type fingerprint sensor. The dielectric thin film tends to be easily broken away or damaged by friction or degradation since the dielectric thin film is a place where the finger print contacts with. Therefore, there is a problem of a low durability of the dielectric thin film.